1. Field of the Invention
The present disclosure herein relates to an imaging system and a method of autofocusing the same.
2. Description of the Related Art
Autofocus (AF) is a function of an optical system automatically focusing on a subject. An AF scheme is largely divided into active and passive schemes. In the active scheme an ultrasonic wave or an infrared ray is emitted to measure a distance to the subject.
In the active scheme, when a glass or other transparent object is interposed between a camera and a subject, the subject is not properly focused because the object reflects the ultrasonic wave or the infrared ray. Also, it is difficult for the optical system in the active scheme to focus on a distant subject due to the limit of a distance that the ultrasonic wave or the infrared ray can reach.
In the passive scheme, a subject is focused on by using a light naturally reflected by the subject. The passive scheme is largely divided into an optical triangulation scheme, a contrast detection scheme, and a phase detection scheme. Here, in the contrast detection scheme, contrast of a portion of an image is continuously calculated while a lens is moved, and, when the contrast becomes a maximum, the image is determined as being in focus.